Ion sources



S. KLEIN ION SOURCES Jan. 24, 1961 2 Sheets-Shea?I 1 T @L 2 N am w N NN um. Y @h1 w w by@ Nh, @oq v hh. 0J h um om wm N V Rm. l I Ilvn. NN. n m ,Mw m N hw /wm En. \\Nm \m\\ w g 1 QN w .WN bm Ow. NJ "RE V 2 E .11. mnu w. LV. l d e l me* WMM/w (as/M BY y a. @KM

Aff.

s. KLEIN 10N soURcEs Jan. 24, 1961 2 Sheets-Sheet 2 Filed April 29, 1959 Eg. E?

United States N SOURCES Siegfried Klein, Paris, France, assignor to Commissariat a IEnergie Atomique, Paris, France The present invention relates to ion sources, that is to say to devices for producing beams of ionized particles for use in various apparatus for the treatment of such particles, such as particle accelerators, mass spectrometers, isotopic separation systems. The invention is more especially concerned with ion sources in which ionization of the particles is obtained by applying a Ihigh frequency electric eld to a chamber, generally made of quartz or glass (in particularvof an aluminum and sodium borosilicate sold under the trademark Pyrex).

In such known ion sources, the high frequency electric field serving to produce ionization is generally obtained in circuits having distributed constants and the ionic yields are low in comparison to the high frequency power brought into play, this being due to the fact that, for a high frequency circuit having distributed constants, the coefficient Q is low and the losses are high.

The object of the present invention is to provide `an ion source intended in particular to ionize gases (such as hydrogen, deuterium, helium, nitrogen) or vapors (for instance vapors of light metals, such as lithium or sodium) to form a beam of ionized particles intended to be fed to a particle accelerator, with a high ionic yield (averaging some ten milliammeters for a high frequency power of approximately 75 watts).

According to the present invention, such an ion source comprises a tube, generally made of glass or quartz, means for producing a high vacuum in said tube, means for applying a high direct potential difference between the two ends of said tube, means for feeding to one end of said tube a substance in the gaseous form to be ionized, and a high frequency current source, and the characteristic feature of this invention consists in the fact that it comprises a resonating cavity energized by said source and producing in a restricted zone thereof a very concentrated electric eld, said tube comprising, in the vicinity of its other end, an enlarged portion in the form of a flat bulb extending transversely to the direction of the bulb, said bulb being disposed in said restricted zone.

Other features of the present invention will become apparent in the following detailed description of a preferred embodiment thereof, with reference to the appended drawings given merely by way of example :and in which:

Fig. 1 is a sectional View of said embodiment of the invention.

Fig. 2 shows the electric lay-out of the ion source of Fig. 1,

Fig. 3 diagrammatically shows the resonating cavity of the ion source of Fig. 1 and the manner in which said cavity is energized.

Fig. 4 illustrates the distributed constant resonating circuit used for energizing the resonating cavity of Fig. 3.

The ion source proper (Fig. l) comprises a tube 1, generally made of Pyrex glass or quartz, said tube having, near one of its ends 24, an enlarged portion in the form of a fiat bulb 2 extending transversely to the direction of the tube, said bulb being of relatively small dimension, for instance having a volume of about one cubic centimeter. The end 24 of tube 1 is supported by a sleeve 3 carried by a conical piece 4 maintained in a housing 25a of a conductor wall 2S. Pieces 3 and 4 are made of metals capable of resisting the impact of ions, such as platinum, stainless steel, aluminum. For linstance, `sleeve 3 is made of platinum and piece 4 of aluminum.

The other end 26 of tube 1 is of conical shape and carries the device T for feeding the gas or vapor to be ionized. This device includes a chamber 27 with two hollow extensions 28 and 29, extension 28 fitting on the end 26 of tube land extension 29 holding a hollow electrode 5 through which is introduced, in the direction of arrow F, the gas or vapor to be ionized. Chamber 27 contains a quartz disc 30 intended to increase the disruptive voltage of the gaseous medium inside the ion source.

Over most of its length, tube 1 is housed in a coaxial resonating cavity R which comprises the following elements:

A central hollow conductor 7 closely surrounding said tube;

A conductor envelope 6 coaxial with said central conductor 7 and located at a distance therefrom;

A metal plate 8, welded at 30 to the external envelope 6 so as to be electrically connected therewith, this plate closing one end of envelope 6 and being provided with a central hole 31 for the passage of the ions produced in bulb 2 `and leaving tube 1 in the direction of arrow f;

A metal plate 34, located at the other end of envelope 6 and welded at 30a thereto, said plate 34 being rigid with a sleeve 35 xed on conductor 7;

Toroidal rubber joints 32 and 33 are inserted between plate 8 and bulb 2 on the one hand, and between said plate 8 and wall 25 on the other hand;

Pumping means, diagrammatically shown at P, communicate with the space 50 between plates 8 and 25 and located on the inside of toroidal joint 33 so as to maintain, through the orices 4a of piece 4, a vacuum ranging from 10-3 to 10-4 mm. of mercury in tube 1.

The feed of current to the elements of the device is shown by Fig. 2.

'There is first produced a high direct potential difference between electrode 5 (positive terminal +HT0) and plate 8 (negative terminal -HT0).

A high frequency voltage is applied to the central conductor 7 of the resonating cavity from an oscillator tube 9 (located in a shielding casing 23) in the following manner: the elements of said oscillator tube 9 (as will be more completely described hereinafter) are connected through conductors 37, 44 and 43, extending through said shielding casing 23, to the upper conducting plates of three capacitors 12, 16 and 18. The under conducting plates of said capacitors are respectively connected, through copper rods 20, 21 and 22, to different points of the central conductor 7. A single sheet of mica 36, of a thickness of about 0.1 mm., forms the dielectric between the respective plates of the three capacitors 12, 16 and 18. In this way, there is obtained a capacitive coupling between the resonating cavity and the oscillator, which permits of imparting very high potentials thereto. The casing 23 of the high frequency source is grounded.

The oscillator tube 9 is for instance a tetrode calcu. lated to consume about -100 watts at a frequency averaging mHz., this tube being fed with a plate high voltage -I-HTl applied to plate 11 through line 10, with a screen high voltage -l-HT2 applied to screen grid 14 through line 13 and with a heating voltage applied to cathode 38 through wires 39, current return taking place through the common line 19 which constitutes the negative terminal -HT ofthe feed high voltages. Choke accesso coils 40 prevent return flow of the high frequency currents produced by tube 9, and capacitors 41, 42 prevent the ow of direct current directly toward line 19. The control grid 15 of tube 9 is connected on the' one lia-nd directly to conductor 43 lead-ing to capacitor 16 and on the other hand, through a resistance 17 of some thousands of ohms, to conductor 44 leading to capacitor 18 which is connected, through conductor 44a, to the return line 19, that is to say to the cathode from the high frequency viewpoint. Finally, the plate voltage is applied, through conductor 37, to capacitor 12. Thus, tube 9 cooperates with resonating cavity R to form an oscillating system as diagrammatically illustrated by Fig. 3.

The numerical values of the elements illustrated by Fig. 2 may be as follows.

through conductors Z0, 21, 22 so as to produce a concentrated high frequency field (as indicated by the lines of force which are spaced apart at 46 and close to one another at 46a in zone S) between the end 45 of conductor 7 and plate 8, which are located at a distance d from each other hardly greater than the thickness e of the bulb. A capacitor C is placed between these two elements, whereas the inside of the envelope 6 of the resonating cavity constitutes the self-inductance L of the oscillating circuit diagrammatically shown on Fig. 4 and corresponding to the structure above described.

The concentration of the lines of force 46a of the electric eld in a restricted zone S of the resonating cavity where, according to the essential feature of the invention, is located the ionization zone constituted by bulb 2, ensures a high ionization of the gas or vapor placed in said bulb. Furthermore, due to the fact that the Q factor of a resonating cavity may be very high for very high frequencies (in opposition to what takes place in distributed constant resonating circuits), it .is possible to start the ionization of the gas or vaporun bulb 2 very easily because the eld is very intensive in this volume before ionization is started. It is thus possible to obtain, with a chamber according to the invention, a Q coecient averaging 1000, which ensures a very easy starting of ionization.

Another very important advantage of the device according to the invention lies in the fact that the ionization zone (bulb 2) is contiguous to the extraction zone, extraction taking place through known means, for instance by means of a series of extraction, acceleration and focussing electrodes (for instance of the type described in the article published in. the number of December 1948 of the periodical, The Review of Scientiiic Instruments, pages 907-909), to direct the ions toward the accelerator or other device making use of these ions.

The operation of the ion source according to the present invention results clearly from the above descripg tion of the structure thereof.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and eicient embodiments of my invention, it should be well understood that I do not Wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended Within the scope of the accompanying claims.

What I claim is:

I. An ion source which comprises, in combination, a tube, means for applying a high direct potential difference between the ends of said tube, said tube having, near one of its ends, an enlarged portion in the form of a flat bulb extending transversely to the direction of said tube, pumping means for exhausting said tube, means for feeding the other end of said tube with a gaseous substance to be ionized, a high frequency current source and means forming a resonating cavity at least a portion of which surrounds said bulb, said cavity being coupled with said source to be energized by it and being arranged to form a zone of concentrated electric field including, and substantially limited to, the volume of said bulb.

2. An ion source which comprises, in combination, a tube, means for applying a high direct potential difference between the ends of said tube, said tube having, near one of its ends, an enlarged portion in the form of a flat bulb extending transversely to the direction of said tube, pumping means for exhausting said tube, means for feeding the other end of said tube with a gaseous substance to be ionized, a resonating cavity constituted by a hollow central conductor closely surrounding said tube from said second mentioned end thereof to said bulb, a conductor casing surrounding said central conductor coaxially thereto and at a distance therefrom, a transverse conductor plate rigid and in electric contact with said central conductor at a point thereof remote from said bulb and located on the same side thereof as said second mentioned end of said tube, said plate being in electric contact with one end of said envelope, a transverse conductor plate rigid and in electric contact with the other end of said envelope extending on the other side of said bulb from said first mentioned plate at a distance from said bulb just a little greater than the thickness thereof, said last mentioned plate being provided with a central opening in line with said tube for the. passage of a beam of ions from said bulb.

3. An ion source according to claim l including a capacitive coupling between said high frequency current source and said resonating cavity.

4. An ion source according to claim l including a capacitive coupling between said high frequency current source and said resonating cavity and a grounded shield casing surrounding said last mentioned source.

5. An ion source which comprises, in combination, a tube, means for applying a high direct potential difference between the ends of said tube, said tube having, near one of its ends, an enlarged portion in the form of a flat bulb extending transversely to the direction of said tube, pumping means for exhausting said tube, means for feeding the other end of said tube with a gaseous substance to be ionized, a resonating cavity constituted by a hollow central conductor closely surrounding said tube from said second mentioned end thereof to said bulb, a conductor casing surrounding said central conductor coaxially thereto and at a distance therefrom, a transverse conductor plate rigid and in electric contact with said central conductor at a point thereof remote from said bulb and located on the same side thereof as said second mentioned end of said tube, said plate being in electric contact with one end of said envelope, a transverse conductor plate rigid and in electric contact with the other end of said envelope extending on the other side of said bulb from said first mentioned plate at a distance from said bulb just a little greater than the thickness thereof, said last mentioned plate be ing provided with a central opening in line with said tube, for the passage of the beam of ions from said bulb, and means for energizing said cavity in resonance, said last mentioned means including three capacitors having each two conducting plates, one of the plates of each of said capacitors being connected with said central conductor, an oscillator tube having a cathode, a

control grid and an anode, said cathode being connected References Cited in the le of this patent with the other plate of one of said capacitors, said grid UNITED STATES PATENTS being connected with the other plate of another of said 6. An ion source according to claim 5 in which said sheet of dielectric material is a mica sheet of a thickness 10 averaging 0.1 millimeter.

UNTTED STATES PATENT OFFICE 'C-ERTIFICATON 0F CRRECTEUN Patent Noo 2,969,480 January 24, 1961 Siegfried Klein It s hereby certified that error appears in the above numbered patent requiring correction and 'that thersad Letters Patent should readas corrected below. f

signed and Sealed this 5th day of september 1961.,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

